1. Field
The present invention relates generally to storage of liquid in Fluid Dynamic Bearing (FDB) motors and more particularly to capillary reservoirs for use in FDB motors.
2. Description of Related Art
Capillary seals are presently used to retain lubricating liquid (e.g., oil) at hydrodynamic bearing surfaces of disc drive motors and to provide a reservoir of lubricating liquid to replace lubricating liquid lost through evaporation and other causes.
Typical capillary seals are formed between radially opposing surfaces of coaxial relatively rotatable motor members, e.g., between an outer surface of a fixed shaft and an inner surface of a rotating hub disposed around the shaft, as shown in FIG. 2a. Typically, either the shaft or the hub is machined so that the radially opposing surfaces form a tapering gap with respect to each other. The gap typically has an annular cross-section, as illustrated in FIG. 2b. The tapering gap functions as a reservoir of lubricating liquid as well as a capillary seal, and therefore the volume of the tapering gap largely determines a reserve amount of lubricating liquid to provide for loss of lubricating liquid. However, higher volumes of lubricating liquid (which may enable longer lived motors) typically require that the tapering gap have a wider annular cross-section, which may reduce the ability of a meniscus of the capillary seal to retain lubricating liquid. What is needed are further ways to store lubricating liquid and supply that lubricating liquid to hydrodynamic bearing surfaces in fluid dynamic bearing motors.